C# GDI渐变 透明窗体，基于GDI技术实现的窗口效果，有渐变效果，不过我发现窗体并没有透明化，呵呵，或许有更高深的意图在里面。-C# GDI gradient transparent form, based on the effect of GDI technology window, there is a gradient effect, but I did not find the form and transparency, Oh, maybe there are more inten